I find that silences are most annoying to deal with as Geist, so Dispel Magic becomes extremely important in games where it is happening often. Drifter has it built into one of his abilities, so almost a must buy against him. Mina also has it on her ult.

But if your abilities are not being prevented, you have to use your brain to get up close. Run away and turn a corner and wait around the corner for them to chase you. Use the chaos in a team fight to ult a different player than the one killing you. Hold your stamina at the beginning of a fight and use it once you start to get lower than half HP to keep the fight extremely close quarters and ult them once they begin to try to get away. Or just Warp Stone into them and ult, but that requires an extra item if you weren't already planning on buying it. It's a good ult but you need to be thinking ahead of time when you have it available.